What zombie in the original game is summoned by Disco Zombie's dance?

The zombie summoned by Disco Zombie’s dance is the Backup Dancer.

In the original Plants vs. Zombies, Disco Zombie periodically performs a dance and calls Backup Dancers into the lawn around him. These summoned zombies move toward the house like ordinary attackers, adding extra bodies to the wave and forcing the player to handle several threats at once.

The name is a direct parody of a stage performer surrounded by supporting dancers. That theme is why the answer is not another named zombie such as Flag Zombie or Zombie Yeti. Disco Zombie is the summoner, while Backup Dancer is the unit created by his special ability. The dancers are therefore a distinct zombie type rather than an alternate name for Disco Zombie.

A nearby detail players often ask about is how the dance affects strategy: the summoned dancers can appear in surrounding lanes, so eliminating Disco Zombie quickly can prevent the formation from becoming more difficult. The game’s broader design gives many zombies a signature gimmick, from pole-vaulting to carrying doors or riding dolphins.